WITH THE MICROSCOPE. /I 



spontaneously from the more oily fatty matters. By the action of acids 

 and other agents many fats are decomposed and the crystalline 

 fatty acids are set free. Many slightly soluble earthy salts crystal- 

 lise under certain circumstances, especially in mucus and viscous 

 fluids in the form of globules or spherules, which often closely resemble 

 oil globules, from which they may be distinguished by their hardness 

 and chemical characters. Seep}. XIX, fig. 114. 



138. For Beginners only. How to Examine an Object in the 

 Microscope. Any one who purchases a microscope probably endea- 

 vours to look at some object through it as soon as it comes home, 

 and of those who make such an attempt many fail completely, 

 because they are not acquainted with the principles enunciated in 

 the preceding pages. The observer should go through the tables- 

 at the end of the volume ; but if too impatient and eager for action, 

 he may proceed to work at once as follows : 



1. Place the microscope in the position represented in fig. 43, 

 pi. X, the eye-piece and the low object-glass (the inch) being 

 adapted to the microscope. Turn the mirror out of the way and 

 permit the dark part of the diaphragm to occupy the field, or place 

 a piece of black paper beneath the aperture. 



2. Take a dry bread crumb; about the size of a small pin's head, 

 place it on a glass slide, and the slide upon the stage of the 

 microscope. 



3. Place an ordinary wax candle, or French, or other lamp in 

 such a position that the upper surface of the crumb of bread may be 

 lighted up, or use the bull's-eye condenser, so that a strong light is 

 condensed upon the object, as in fig. 43. 



4. Screw down the body of the microscope until the object 

 comes into focus and is seen distinctly. 



The crumb of bread is examined as an opaque object by reflected 

 light, and peculiarities of its surface are alone made out. 



5. Alter the position of the lamp, if necessary, and so arrange the 

 mirror that the light may be reflected from it, and caused to pass 

 through the object (transmitted light), fig. 42, pi. X. Prevent the 

 light from illuminating the surface as before. The object seems very 

 dark and little that is definite can be discovered. 



6. Break the crumb up into several smaller pieces. This may be 

 easily effected with the aid of a penknife. Most of the particles 

 appear angular. They seem dark because they are too thick for 

 the light to pass through them, but here and there one appears more 

 or less transparent. 



7. One of the transparent pieces being in the field, remove the 

 inch power and screw on the quarter of an inch object-glass, and 



